CANTILEVERS STRUCTURES

Cantilevers resist lateral load primarily in bending.  They may consist of single towers or  multiple towers.  Single towers act much like trees and require large footings like tree  roots to resist overturning.  Bending in cantilevers increases from top down, justifying  tapered form in response.

1  Single tower cantilever
2  Single tower cantilever under lateral load
3  Twin tower cantilever
Twin tower cantilever under lateral load
5  Suspended tower with single cantilever
6  Suspended tower under lateral load

Shear Walls Systems

As the name implies, shear walls resist lateral load in shear.  Shear walls may be of wood, concrete or masonry.  In the US the most common material for low-rise  apartments is light-weight wood framing with plywood or particle board sheathing. Framing studs, spaced 16 or 24 inches, support gravity load and sheathing resists lateral  shear.  In seismic areas concrete and masonry shear walls must be reinforced with steel  bars to resist lateral shear.

1  Wood shear wall with plywood sheathing
2  Light gauge steel shear wall with plywood sheathing
3  Concrete shear wall with steel reinforcing
4  CMU shear wall with steel reinforcing
5  Un-reinforced brick masonry (not allowed in seismic areas)
8  Two-wythe brick shear wall with steel reinforcing


VERTICAL SYSTEMS STRUCTURES

Vertical systems transfer the load of horizontal systems from roof to foundation, carrying  gravity and/or lateral load.  Although they may  resist gravity or lateral load only, most  resist both, gravity load in compression, lateral load in shear.  Walls are usually designed  to define spaces and provide support, an appropriate solution for apartment and hotel  buildings.  The four systems are:

1  Shear walls (apartments / hotels)
2  Cantilever (Johnson Wax tower by F L Wright)
Moment frame
4  Braced frame



A  Concrete moment resistant joint Column re-bars penetrate beam and beam re-bars penetrate column)  B  Steel moment resistant joint (stiffener plates between column flanges resist beam flange stress)



VERTICAL STRUCTURES

Vertical elements

Vertical elements transfer load from roof to foundation, carrying gravity and/or lateral  load.  Although elements may resist only gravity or only lateral load, most are designed to  resist both.  Shear walls designed for both gravity and lateral load may use gravity dead  load to resist overturning which is most important for short walls.  Four basic elements  are used individually or in combination to resist gravity and lateral loads

1  Wall under gravity load
2  Wall under lateral load (shear wall)
3  Cantilever under gravity load
4  Cantilever under lateral load
5  Moment frame under gravity load
6  Moment frame under lateral load
7  Braced frame under gravity load
9  Braced frame under lateral load